#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int N = 1;
const int M = 1e9+7;

set<string> s{"ABC", "ARC", "AGC", "AHC"};

int main()
{
#ifdef LOCAL
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
#endif
    ios::sync_with_stdio(false), cin.tie(0);
    string a;
    for (int i = 1; i <= 3; i++) {
        cin >> a;
        s.erase(a);
    }

    cout << *s.begin() << endl;
    
    return 0;
}